There were updates offered by Ubuntu and I installed them. After that the Ubuntu desktop GUI hasn't been working correctly and it freezes frequently. Moreover, instead of having the Ubuntu startup screen like below, only a blank gray screen comes, then on the desktop instead of wallpaper, only a black background is applied.
I also tried this
sudo apt-get install ubuntu-desktop but get thee results shown below.
The following packages have unmet dependencies: ubuntu-desktop : Depends: checkbox-gui but it is not going to be installed Recommends: python3-aptdaemon.pkcompat but it is not going to be installed Recommends: unity-webapps-common but it is not going to be installed E: Unable to correct problems, you have held broken packages.
I tried to install
checkbox-gui, then it gives another unmet dependencies error message, than another then another.